理由：越来越多的证据表明 miRNA-21 (miR-21) 上调与肿瘤发病机制密切相关。然而，miR-21 抑制调节免疫抑制肿瘤微环境 (TME) 和提高肿瘤对免疫检查点阻断疗法的敏感性的机制在很大程度上仍未被探索。在这项研究中，我们证明了使用 PD-L1 靶向肽缀合物 (P21) 将抗 miR-21 精确递送至 PD-L1high TME。方法：研究 miR-21 抑制机制涉及进行定量实时 PCR、蛋白质印迹、流式细胞术和共聚焦显微镜分析。在携带 CT26.CL25 肿瘤和 4T1 乳腺癌的小鼠模型中评估了 P21 单一疗法或联合抗 PD-L1 免疫检查点抑制剂的抗肿瘤功效和免疫特征。结果 P21 抑制癌细胞中的致癌 miR-21，可有效激活抑癌基因，诱导自噬和内质网应激。随后的细胞死亡相关免疫激活（免疫原性细胞死亡）是通过释放损伤相关分子模式启动的。体内结果还表明，P21引发的免疫原性细胞死亡可以有效地使免疫抑制性TME变得敏感。也就是说，P21通过赋予垂死的癌细胞免疫原性并促进树突状细胞成熟来增强肿瘤组织中的CD8 T细胞浸润。同时，将 P21 与抗 PD-L1 免疫检查点抑制剂相结合，在 CT26.CL25 荷瘤小鼠模型和 4T1 转移性肿瘤模型中产生高效的抗肿瘤作用。结论：总的来说，我们通过将抗 miR-21 精确递送至 PD-L1high TME，阐明了 miR-21 相关的免疫原性细胞死亡机制。这些发现凸显了 miR-21 作为免疫治疗干预靶标的潜力。© 作者。

Rationale: Growing evidence has demonstrated that miRNA-21 (miR-21) upregulation is closely associated with tumor pathogenesis. However, the mechanisms by which miR-21 inhibition modulates the immunosuppressive tumor microenvironment (TME) and improves tumor sensitivity to immune checkpoint blockade therapies remain largely unexplored. In this study, we demonstrate the precise delivery of anti-miR-21 using a PD-L1-targeting peptide conjugate (P21) to the PD-L1high TME. Methods: Investigating miR-21 inhibition mechanisms involved conducting quantitative real-time PCR, western blot, flow cytometry, and confocal microscopy analyses. The antitumor efficacy and immune profile of P21 monotherapy, or combined with anti-PD-L1 immune checkpoint inhibitors, were assessed in mouse models bearing CT26.CL25 tumors and 4T1 breast cancer. Results Inhibition of oncogenic miR-21 in cancer cells by P21 efficiently activates tumor suppressor genes, inducing autophagy and endoplasmic reticulum stress. Subsequent cell-death-associated immune activation (immunogenic cell death) is initiated via the release of damage-associated molecular patterns. The in vivo results also illustrated that the immunogenic cell death triggered by P21 could effectively sensitize the immunosuppressive TME. That is, P21 enhances CD8+ T cell infiltration in tumor tissues by conferring immunogenicity to dying cancer cells and promoting dendritic cell maturation. Meanwhile, combining P21 with an anti-PD-L1 immune checkpoint inhibitor elicits a highly potent antitumor effect in a CT26.CL25 tumor-bearing mouse model and 4T1 metastatic tumor model. Conclusions: Collectively, we have clarified a miR-21-related immunogenic cell death mechanism through the precise delivery of anti-miR-21 to the PD-L1high TME. These findings highlight the potential of miR-21 as a target for immunotherapeutic interventions.© The author(s).